1. Field of the Invention
The present invention relates to the simulation of radiation therapy and in particular, to a system which is able to simulate dynamic treatment regimes.
2. Brief Description of the Related Art
Fractionated conformal radiotherapy, such as intensity-modulated radiotherapy, that employs computer-controlled multi-leaf collimators, requires accurate beam placement in reference to the patient's anatomy. Beam placement and beam apertures are defined based on either CT simulation (beam's eye view planning) or conventional RF simulation. After the completion of the treatment plan, the treatment fields and their corresponding blocks (defined either by the multi-leaf collimator (MLC) or cerroband block) need to be verified prior to the treatment both for isocenter placement and for the shape of the MLC block. Currently, this check is done at the conventional simulator, which is not outfitted with an MLC. Consequently, the MLC pattern cannot be verified at the time of the port verification process prior to treatment. The aperture verification has to be repeated at the linac using a port imaging technique (port-film or electronic portal imaging device (EPID)). The drawbacks of this practice are that this process is not efficient as the filming has to be repeated several times, especially if shifts or corrections need to be applied; it does not allow for beam aperture verification at the conventional simulator; it can potentially increase the cost of treatment; and it can disrupt the patient's treatment schedule with unnecessary delays.
Varian Medical Systems, has a product that allows for the MLC shapes from a plan to be exported to the conventional simulator and to be visualized on top of a fluoroscopic static image. However, the Varian system cannot simulate dynamic treatment regimes.
It is therefore desirable to be able to project static and dynamic MLC plan images onto radiographic and fluoroscopic (RF) images for beam aperture verification prior to treatment.
It is also desirable to be able to simulate respiration-gated treatment regimes. In order to do so, it is necessary for simulation images to be correlated with the patient's respiratory cycle. U.S. Pat. No. 6,690,965 discloses a method and system for physiological gating for radiation therapy in which an optical or video image systems measures regular physiological movement of the patient's body. A gating signal is generated to suspend delivery of radiation upon certain threshold events detected in the physiological movement.